A multiplex system (10) includes a master controller (20) and a plurality of remote stations (50) which are connected together by a cable (90). The cable (90) is a twin coax cable which includes data and clock conductors (94, 92) which are surrounded by power and ground conductors (98, 100). The power and ground conductors (98, 100) are capacitively coupled such that the power conductor (98) simultaneously transmits power and provides an effective shield. The master controller (20) includes a microcomputer (22) which in turn includes an UART (30). The UART (30) is used to transmit command bits to the remote stations (50) while the CPU (23) reads response bits from the remote stations (50) in order to allow response bits to be interleaved in time with command bits. In one embodiment, the command bits are used to strobe row conductors (72) of a keyboard (70) and the response bits are used to monitor column conductors (74) of the keyboard (70) to allow a keyboard (70) to be controlled by the master controller (20) in a simple and efficient manner. In the preferred ambodiment an integration counter is used to decode response signals such as those from a keyboard and the integration counter is incremented when the desired signal is obtained and decremented when it is not. In this way the state of the signal can be determined even in an extremely noisy environment.